1. Field of Invention
This invention relates to a method for controlling and recovering hydrocarbon or certain low-polarity organic chemicals.
2. Brief Statement of the Prior Art
Hydrocarbon fuel, oil, and chemical spills occur frequently on a multitude of surfaces. On land, clay sorbents, cellulose or sphagnum products, surfactants, or other bioremedial methods to name a few are used in these situations with the intent of cleaning up the spill in a quick fashion or bioremediating a contaminated soil surface over time. On the water, spills tend to present unique problems and require the responders to assess each spill quickly and choose among a variety of spill response products such as absorbents, adsorbents, gelling agents, sinking agents, surface washing agents, dispersants, biodegradation agents, biodegradation enhancers, de-mulsifiers, herding agents and approaches such as in situ burning. Factors such as cold water or broken ice conditions can change the physical state of crude oils making broad application of chemical dispersants more difficult and ineffective.
Various techniques and materials have been used as absorbents in helping to minimize contamination resulting from hydrocarbon fuel, oil, and chemical spills. Absorbents generally function by attracting materials to their pore spaces. Adsorbents such as polypropylene fibers function by hydrophobic nature in water and oleophilic attraction of the oil to wick into the surface area of the fiber.
Furthermore, various elastomeric materials of the prior art are disclosed regarding A-B-A triblock elastomers for hydrocarbon absorption during environmental cleanup on water. The A-B-A elastomers currently utilized include Styrene-Butadiene-Styrene, SBS or Styrene-Isoprene-Styrene, SIS (U.S. Pat. No. 3,518,183), Styrene-Butadiene-Styrene/Ethylene-Propylene Diene Monomer, SBS/EPDM (U.S. Pat. No. 6,344,519), Styrene-Ethylene-Butylene-Styrene, SEBS (U.S. Pat. No. 4,941,978 and U.S. Pat. No. 5,104,548), or Styrene-Ethylene-Propylene-Styrene, SEPS (U.S. Pat. No. 6,056,805).
Many of the prior art copolymers used in spill cleanup, due to their absorbent properties, are of the SEBS type copolymer. A SEBS type copolymer is a polystyrene-poly(ethylene/butylene)-polystyrene copolymer. Examples are KRATON G-1650 or KRATON G-1651 or KRATON G-1652 made by Shell Chemical Company. The KRATON G series, produced by anionic polymerization, are block polymers in which the elastomeric portion of the molecule is a saturated olefin polymer of the type ethylene/butylenes.
However, while the current triblock elastomers have been useful in containing spills, there remains a need for absorbents that have improved elasticity and tensile strength over the prior art with comparable softness. Moreover, there is a need for materials that reduce or eliminate oil bleed during spill absorption. Finally, there is a need for materials that can accomplish the aforementioned goals while remaining cost effective.
Thermoplastic elastomers are a class of polymers that behave like thermoset rubber except that above their melt or softening temperatures are melt processable via thermoplastic processing methods. Unlike thermoset rubber, they can be easily reprocessed and remolded. The ability to process these materials with thermoplastic methods allows for design and fabrication freedom that thermoset rubber does not offer.
The block co-polymers of this patent application are comprised of blocks of crystalline and amorphous domains along the same polymer chain. The crystalline domain acts as the crystalline portion that give thermoplastic elastomers their thermoplastic character and the hydrogenated olefin amorphous domain provides the elastomeric character. Crystalline domains are typically referred to as the “hard” phase and the amorphous domains as the “soft” phase. While both phases contribute to the overall physical and mechanical properties of a thermoplastic elastomer, some key properties may be associated with one phase or the other.
Thermoplastic elastomers are often injection molded to form objects of practical use such as food and beverage containers or soft toy parts, just to name a few examples. Injection molding is the process of melting the plastic to flow inside a barrel and injecting the melt into a mold cavity, where it cools until it keeps the shape of the cavity. Injection molding offers many advantages to alternative manufacturing methods, including minimal losses from scrap since scrap pieces can be melted and recycled, and minimal finishing requirements.
“Compression” refers to the process or result of pressing by applying force on an object, thereby increasing the density of the object. The ability of a material to return to its original shape after being subjected to a predetermined compressive strain or load is known as “compression set”. Specifically, when compression is applied to a structure, it displays elastomeric properties and will essentially recover to its original position upon relaxation. Compression set is sometimes used to describe such elastic recovery. Softness, flexibility, elasticity, and resiliency are also demonstrated through compression set resistance as measured by ASTM D3575. Compression set is reported as a percent of compression that is not recovered. Rink (U.S. Pat. No. 6,344,519) claims for the SBS-EPDM polymer blends that bulk densities greater than 0.75 g/cc tend to prevent the oil from entering formed bodies, while bulk density smaller than 0.45 g/cc cause the bodies to fragment, either when dry or after absorbing oil.
Compression molding consists of a top and bottom plate mold that is machined to a custom configuration. The elastomer is added between the plates and the plates are compressed under heat and pressure for a specific amount of time. The heat applied is usually at or above the melt point of the polymer. After the elastomer is cured properly, the mold is opened, the part is removed, the mold cleaned and the cycle repeated.
U.S. Pat. No. 6,344,519 and U.S. Pat. No. 7,048,878 to Rink, et al. is a process for forming an oil-sorbent composition of matter with bound combinations of styrene-butadiene-styrene (SBS) and ethylene propylene diene monomer (EPDM) as a binder material. The process utilizes an extrusion process or a compression molding process. Rink formed cylindrical bodies between two and about five centimeters across the outer diameter with a hole about one to two centimeters in diameter along the longitudinal axis. The length of the cylinder was seven centimeters corresponding to an outside diameter of 3 centimeters. The EPDM copolymer with a lower melt temperature than the SBS block copolymer acts as a binder, holding the SBS particles together without significantly damaging the physical structure of the SBS block copolymer, thereby reducing the ability of the SBS to absorb hydrocarbons. However, the EPDM, present at 10-30 weight percent, is not as efficient as SBS in oil absorption. In fact, the SBS block copolymer is generally deemed inferior to the SEEPS triblock polymer for absorbing and retaining hydrocarbons in the amorphous matrix. According to Tony M. Pearce (US 2006/0194925) relating to gelatinous elastomer products, “Most makers of gelatinous elastomer materials and articles today express a strong preference for gels made with SEEPS rather than SEBS due to superior strength and elongation, reduced oil bleed, and other desirable material properties.”
In order to melt process the Kraton D SBS block copolymer in U.S. Pat. No. 7,172,721 to make doll heads, Wong used the normal processing temperatures in the range of 175-200° C. at 400-700 psi. These conditions are in the recommended range prescribed by the Shell Chemical Technical Bulletin, SC:455-96 for melt processing of Kraton D polymers. In U.S. Pat. No. 7,122,603, Ikeda describes an injection or compression molding process for thermoplastic elastomer compositions which whereby the molded composition exhibits greatly suppressed compression set and satisfactory tensile strength while exhibiting low hardness. Although the pressures associated with the invention are not disclosed, the temperature was referenced at 284° F.
To achieve optimal bond strength, higher than normal melt temperatures are often required for thermoplastic elastomers. In some critical applications, this temperature can be close to the upper processing temperature limits for the TPE. Melt temperatures of 400-460° F. are common.
Compression molding is used primarily for composite parts and thermoset resins involving a curing process. It is also employed to process thermoplastic resins. Generally speaking compression molding of thermoplastic elastomers requires that the mold temperature be at or around the melt temperature of the polymer. Anything less leads to undesirable product properties. A need, however, exists in the art to form an elastomeric block copolymer, such as the described polymers of the present disclosure, at temperatures and pressures well below what might be expected in order to form typical products of utility through compression molding processes.